U.S. Pat. No. 3,719,489 describes and claims photographic processes employing certain potographically inert compounds which are capable of undergoing cleavage in the presence of the imagewise distribution of silver ions made available during processing of a silver halide emulsion to liberate a reagent, such as, a photographically active reagent or a dye in an imagewise distribution corresponding to that of said silver ions. In one embodiment disclosed therein, color images are produced by using as the photographically inert compounds, color-providing compounds which are substantially non-diffusible in the photographic processing composition but capable of undergoing cleavage in the presence of the imagewise distribution of silver ions and/or soluble silver complex made available in the undeveloped and partially developed areas of a silver halide emulsion as a function of development to liberate a more mobile and diffusible color-providing moiety in an imagewise distribution corresponding to the imagewise distribution of said ions and/or said complex. The subsequent formation of a color image is the result of the differential in diffusibility between the parent compound and liberated color-providing moiety whereby the imagewise distribution of the more diffusible color-providing moiety released in the undeveloped and partially developed areas is free to transfer.
Compounds disclosed as useful in liberating a reagent in the presence of said silver ions and/or silver complex are sulfur-nitrogen compounds containing the group ##STR1## These 1,3-sulfur-nitrogen compounds may be linear or cyclic in structure, and in a particularly preferred embodiment are thiazolidine compounds, such as, compounds which comprise a dye radical having the chromophoric system of an azo, anthraquinone, phthalocyanine or other dye and a thiazolidin-2'-yl moiety which may be bonded directly to the dye radical or through an appropriate linking group.
U.S. Pat. No. 4,098,783, a continuation-in-part of Ser. No. 465,694, now abandoned, which is a division of said U.S. Pat. No. 3,719,489 discloses that dyes substituted with a thiazolidin-2'-yl moiety may be synthesized by condensing a dye possessing an aldehyde group with a 2-aminoethanethiol, or rather than forming the thiazolidin-2-yl moiety as the final step in the synthesis, an intermediate possessing an aldehyde group may be condensed with the selected 2-aminoethanethiol and the condensation product then reacted with the appropriate molecule or molecules to yield the final dye product. For example, an intermediate comprising a linking group substituted with a thiazolidin-2'-yl moiety may be synthesized from a selected aldehyde in several steps including the condensation with a 2-aminoethanethiol and the linking group then reacted as an amine with a dye radical possessing, e.g., a sulfonyl chloride substituent or it may be reacted as a sulfonyl chloride with a dye radical possessing an amino substituent.
The sodium salt of 5-sulfosalicylaldehyde and its synthesis from 5-sulfosalicy lic acid has been reported by H. Weil and K. Brimmer, Chem. Ber., 55, p. 302 (1922). In the procedure described by these authors, 5-sulfosalicylaldehyde was prepared by reducing sulfosalicy lic acid with sodium amalgam, treating the reduction product with aniline to precipitate it as a Schiff base, and after strongly acidifying with hydrochloric acid, isolating the sulfonated aldehyde as its sodium salt using sodium chloride. The preparation of various sulfo-substituted compounds by the sulfonation of aromatic hydrocarbons with concentrated sulfuric acid, fuming sulfuric acid and other sulfonation reagents also is known. G. W. Kirker, OPPI Briefs, Vol. 12, Nos. 3-4 (June-August 1980) pp. 246-249 has reported the synthesis of the sodium salt of 5-sulfosalicylaldehyde by sulfonation of salicylaldehyde with 95% surfuric acid at 40.degree. C. followed by careful dilution of the reaction mixture with water, neutralization with sodium carbonate and isolation of the salt after reducing the volume of the reaction mixture by about one-half.
Also, it is known that sulfo-substituted compounds, either as the free sulfonic acid or in the form of a salt, may be converted to the corresponding sulfonyl chloride by treating with phosphorus chlorides or with an excess of thionyl chloride. Though these reagents have been generally useful in these and in various other conversion reactions to give the desired chlorides, some exceptions have been noted. For example, Roger D. Westland et al., J. Med. Chem., Vol. 16, No. 4, p. 328 (1973) report that "3-Thiazolidinealkanol hydrochlorides IV suspended in THF were readily converted (SOCI.sub.2) to alkyl chlorides V." but that "Other solvents or lack of solvent led to decomposition of the sensitive thiazolidine ring."